Electrical switches, such as relays, are known in the art. Patents U.S. Pat. No. 6,911,884 B2 and U.S. Pat. No. 8,138,863 B2 each disclose an electrical switch having a solenoid, a movable armature, an armature shaft attached to the movable armature, a contact assembly with a plurality of contacts, and other components. The contact assembly is located in a switching chamber region such that any electrical arcs which may arise can be sealed off from an electromagnetic drive system. The contact assembly is attached to the armature shaft, which penetrates a covering plate at a contact chamber aperture. The armature shaft is attached to the armature such that a movement of the armature is also transmitted to the contact assembly.
Due to mechanical tolerances in the overall design and contact wear from electrical arcs, the contacts of the contact assembly never touch corresponding mating contacts at the same time. Such a premature, one-sided mechanical contact initiates a force eccentric to the axis of a guide guiding motion of the armature. The spacing between the end of the armature shaft and the prematurely contacted contact acts as a lever, which tilts the guide. Since such an electrical switch is used to switch large loads, the contact forces for switching are high, leading to large radial forces transmitted by the lever to the guide. These forces can lead to wear on bearing surfaces of the guide or may even lead to the locking of the guide.
A locking of the guide can be avoided if the lever follows the condition (A/L)×2μ≦1, with A being the lever length, L the bearing length, and μ the friction factor.
Elongating the bearing length can prevent locking but impairs the shock resistance of the electrical switch. The contact chamber aperture can be used as a second bearing surface, however, this would require precise mechanical tolerances to avoid a lateral offset of the two bearing surfaces, which would lead to locking.
Locking may also be prevented by reducing the friction factor. However, reducing the friction factor is only possible to a limited extent and requires expensive bearing coatings such as polytetrafluoroethylene (PTFE). Furthermore, such a coating can become worn over the lifespan of the electrical switch, increasing the friction factor over time.